In telephone or other telecommunication systems, especially those partially operating by pulse-code modulation (PCM), problems arise in the conversion of analog signals, arriving at an exchange from stations not operating in the PCM mode, into digital form for handling by the processor of the exchange. If the analog signals are numerical pulses of the aforementioned multifrequency-coded type, their evaluation in the available time slots involves a large number of operations such as threshold determinations to be performed in each signaling channel. The complexity of the equipment heretofore needed for this purpose has limited the extent to which time-division multiplexing (TDM) is available at such an exchange. An alternative sometimes resorted to in the past, i.e. the digitization of incoming analog signals for switching purposes and their subsequent reconversion to analog form for evaluation, entails even more complex circuitry.